• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.561-565
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• 2002

The effects of sintering additives such as $Bi_2O_3$ and $V_2O_5$ on the microwave dielectric and sintering properties of (Zn, Mg)$TiO_3$ system were investigated. Highly dense samples were obtained for $(Zn_{0.8}Mg_{0.2})TiO_3$ at the sintering temperature range of $870{\sim}900^{\circ}C$ with $Bi_2O_3$ and $V_2O_5$ additions of <1wt.%, respectively. The microwave dielectric properties of $(Zn_{0.8}Mg_{0.2})TiO_3$ with 0.45 wt.% $Bi_2O_3$ and 0.55 wt.% $V_2O_5$ sintered at $900^{\circ}C$ were as follows: $Q{\times}f_o$=56,800 GHz, ${\varepsilon}_r$=22, and ${\tau}_f=-53ppm/^{\circ}C$. In order to improve temperature coefficient of resonant frequency, $TiO_2$ was added to the above system. The optimum amount of $TiO_2$ was 15 mol.% when sintered at $870^{\circ}C$, at which we could obtain following results: $Q{\times}f_o$ = 32,800 GHz, ${\varepsilon}_r$ = 26, and $\tau_f=0ppm/^{\circ}C$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.131-134
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• 2002

The effect of the addition on the densification, low temperature sintering, and microwave dielectric properties of the Ca[($Li_{1/3}Nb_{2/3}$)$_{1-x}$$Ti_{x}$]$O_{3-{\delta}}$/(CLNT) was investigated. $Bi_2O_3$ additives improved the dencification and reduced the sintering temperature from $1150^{\circ}C$ to $900^{\circ}C$ of CLNT microwave dielectric ceramics. As increasing $Bi_2O_3$ contents, the dielectric constants and bulk density were increased. The quality factor, however, was decreased slighty. The temperature coefficients of the resonant frequency shifted positive value as increasing $Bi_2O_3$ contents. The dielectric properties of Ca[($Li_{1/3}Nb_{2/3}$)$_{1-x}$$Ti_{x}$]$O_{3-{\delta}}$ and Ca[($Li_{1/3}Nb_{2/3}$)$_{0.8}Ti_{0.2}$]$O_{3-{\delta}}$ with 5wt% $Bi_2O_3$ sintered at $900^{\circ}C$ for 3h were $\varepsilon_{r}$=20, 35 Q.$f_{0}$=6500, 11,000 GHz, $\tau_{f}$=4, 13 ppm/$^{\circ}C$, respectively.

• 한국세라믹학회지
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• 제34권4호
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• pp.368-372
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• 1997

The microwave dielectric properties of (1-x)La2/3TiO3-xLaAlO3 system in which LaAlO3 having $\varepsilon$r$\geq$90 and positive $\tau$f was investigated. The crystal system of (1-x)La2/3TiO3-xLaAlO3 was pseudo-cubic in the range of 0.1$\leq$x$\leq$0.07. Its lattice constant increased with increasing x in spite that the amount of LaAlO3 containing of smaller Al(0.57 $\AA$) ion than Ti(0.64 $\AA$) increased. As the amount of LaAlO3 increased from x=0.1 to 0.9, the relative dielectric constant ($\varepsilon$r) decreased from 50 to 23 and the temperature coefficient of resonant frequency($\tau$f) decreased from +84 to -50. On the other hand, the value of Q.f0 reached a maximum (148,000 at 7 GHz) at x=0.7, where a rapid increase in the peak intensity of XRD occured, and further increased after prolonged sintering. The microwave dielectric properties of $\varepsilon$r=37, Q.f0=47,000 (at 7 GHz), and $\tau$f=-2 ppm/$^{\circ}C$ were obtained near 0.6La2/3TiO3-0.4LaAlO3 (x=0.4) composition.

• 대한치과기공학회지
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• 제40권1호
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• pp.33-40
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• 2018

Purpose: The purpose of this study was to investigate the influence of mechanical properties of various ultra-dental stone by setting methods. Methods: 240 cylinder specimens($10mm{\times}20mm$) were prepared from three ultra-dental stones(Gemma, Die keen and Fuji rock; n = 80) in accordance with the manufacturers' recommendations. Half of the specimens of each stone(n = 40) were dried in open air within a room temperature; the other half(n = 40) underwent in a silicone rubber mold in open air for 30 minutes and then were dried in a microwave oven for 10 minutes to 600W. Compressive strength(CS), compressive modulus(CM) and diametral tensile strength(DTS) conducted until fracture using Instron 5966 at each of the following periods: 1 and 24 hours from mixing. One-way analysis of variance and Scheffe's post hoc test were performed for statistical comparisons at a significance level of P<.05. Results: The CS and CM values in all dental stone indicated highest after 24h(54.25 MPa < ) than the values for specimens dried in microwave method. The DTS values revealed the highest microwave method. However, in 24h, FJ(Fu-ji rock) and GM(Gemma) had lower mechanical properties than air. Conclusion : Within the limitations of this study, CS did not influence by microwave method but DTS affected according to the setting.

• 한국전기전자재료학회논문지
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• 제16권11호
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• pp.975-978
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• 2003

The microwave dielectric properties and the microstructures on B $i_{0.97}$T $m_{0.03}$Nb $O_4$ doped with $V_2$ $O_{5}$ were systematically investigated. B $i_{0.97}$T $m_{0.03}$Nb $O_4$ ceramics sintered at 920-96$0^{\circ}C$ were mainly consisted of orthorhombic and triclinic phases after addition of $V_2$ $O_{5}$. The apparent density increased slightly with increasing the $V_2$ $O_{5}$ addition. The dielectric constants($\varepsilon$$_{r}$) also increased with $V_2$ $O_{5}$ addition(30-45). The Q${\times}$ $f_{0}$ values measured on B $i_{0.97}$T $m_{0.03}$Nb $O_4$ ceramics doped with $V_2$ $O_{5}$ were between 2,000 and 12,000[GHz] when the sintering temperatures were in the range of 920-960[$^{\circ}C$]. It was confirmed that the temperature coefficient of the resonant frequency($\tau$$_{f}$) can be adjusted from a positive value of +10ppm/$^{\circ}C$ to a negative value of -15ppm/$^{\circ}C$ by increasing the amount of $V_2$ $O_{5}$ Based on our experimental results, the B $i_{0.97}$T $m_{0.03}$Nb $O_4$(added $V_2$ $O_{5}$) ceramics can be applied to multilayer microwave devices at low sintering temperatures.ng temperatures.emperatures.ratures.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
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• pp.350-353
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• 2002

The microwave dielectric properties and the microstructures on $Bi_{0.97}Nb_{0.03}O_{4}$doped with $V_{2}O_{5}$ were systematically investigated. $Bi_{0.97}Tm_{0.03}Nb_{0.03}O_{4}$ ceramics sintered at $920-960^{\circ}C$were mainly consisted of orthorhombic and triclinic phases after addition of $V_{2}O_{5}$. The apparent density increased slightly with increasing the $V_{2}O_{5}$ addition. The dielectric $constants(\varepsilon_r)$ also increased with $V_{2}O_{5}$ addition(30-45). The $Q{\times}f_0$ values measured on $Bi_{0.97}Tm_{0.03}NbO_4$ ceramics doped with $V_{2}O_{5}$ were between 2,000 and 12,000[GHz] when the sintering temperatures are in the range of $920-960[^{\circ}C]$. It was confirmed the temperature coefficient of the resonant $frequency(\tau_f)$ can be adjusted from a positive value of $+10[ppm/^{\circ}C]$ to a negative value of $-15ppm/^{\circ}C$ by increasing the amount of $V_{2}O_{5}$. Based on our experimental results, the Bi0.97Tm0.03NbO4(added V2O5) ceramics can be applied to multilayer microwave devices at low sintering temperatures.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.653-656
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• 1999

Effect of $Al_2O_3$ Additives on Microwave Dielectric Properties of $0.15(Ba_{0.85}Ca_{(0.15-y)}Mg_y)$-0.125 $Nd_2O_3-0.60TiO_2+10wt%Bi_zO_3$ (y=0.05, 0.08) Ceramics was investigated. To control of $\tau\;{f}$ on microwave dielectric properties of $0.15(Ba_{0.85}Ca_{(0.15-y)}Mg_y)$-0.125 $Nd_2O_3-0.60TiO_2+10wt%Bi_zO_3$ ceramics $Al_2O_3$ was doped in the composition range of 0 to 0.15 wt%. As a result, dielectric constant was decreased from 94 to 80 but $Q\cdot{f}_0$ value was increased from 4980 to 5210 GHz and temperature coefficient of resonant frequency can be controlled from +9 to -10$ppm^\circ{C}$ as an increase of$Al_2O_3$ doping concentration. Especially, a new microwave dielectric material having $\varepsilon\;_r=84,\;Q\cdot{f}_0=5120\;GHz\;and\;\tau_f=0\;ppm/^\circ{C}$ was obtained at $Al_2O_3$ doping concentration of 0.08 wt%.

• Elastomers and Composites
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• 제53권3호
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• pp.124-130
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• 2018

Recently, microwaves have been used for desulfurization because they can selectively dissociate C-S and S-S bonds present in vulcanized rubber. In this study, we investigated the changes in structural and physical properties of EPDM (Ethylene propylene diene monomer) rubber by irradiating it with microwaves for different durations. The surface chemical composition of the irradiated EPDM rubber was analyzed by FT-IR, XPS, and EDS analyses. It was confirmed by XPS that C-S and S-S S2p peak heights greatly decreased when microwave irradiation was performed for more than 5 min. In the EPDM sample irradiated with microwaves for 10 min, the number of S-O bonds significantly increased owing to oxidation. As the microwave irradiation time was increased, SEM images showed cracks and voids on the EPDM surface. The 20% decomposition temperature of the EPDM rubber sample was investigated by TGA, and it was found to be about $435.23^{\circ}C$ for the EPDM rubber irradiated for 10 min. The crosslinking density of the EPDM rubber was determined by measuring the degree of swelling, and the highest value was observed for the E5 sample irradiated for 5 min. The degree of swelling of the E10 sample irradiated for 10 min was lower than that of the E5 sample. These results indicate that when irradiated with microwaves for more than a certain time, desulfurization occurs and the side chain of the EPDM rubber dissociates and forms additional crosslinking bonds.

• 한국세라믹학회지
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• 제35권8호
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• pp.775-782
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• 1998

This experiment is third study concerning BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} (Ln=Sm, Nd, Pr, La..) system which is known to show a high dielectric constant and Q value in microwave dielectric materials. The process of cry-stallization and the microwave dielectric properties of the specimens sintered at 1220-140$0^{\circ}C$ for 2 hr was investigated in the BaO-(Na,{{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} as well as BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} system. The single phase BaPr2Ti5O14 and Ba(Nd,{{{{ { { Pr})_{2 }O }_{3 } }}Ti5O14 was finally formed from the Pr2Ti2O7 (Nd, Pr)2Ti2O7 as a secondary phase in the BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} and BaO-(Nd, {{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} system respectively The dielectric constant of the specimens sint-ered at 1280~131$0^{\circ}C$ showed the maximum value as 105(BaO-{{{{ { { Pr}_{ 2} O}_{3 } }}-{{{{ { TiO}_{2 } }} system) and 88 (BaO-(Nd,{{{{ { { Pr})_{2 }O }_{3 } }}-{{{{ { TiO}_{2 } }} system) and the Q values of them showed higher value than 1800 which are due to the maximum den-sity. However the dielectric properties of the specimens sintered at higher temperature than 131$0^{\circ}C$ were reduced due to the increases of pore which were resulted from the sudden grain growth.

• 한국전기전자재료학회논문지
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• 제15권1호
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• pp.30-36
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• 2002

The effects of the sintering additives such as B $i_2$ $O_3$ and $V_2$ $O_{5}$ on the microwave dielectric and sintering properties of ZnTi $O_3$ system were investigated. Highly dense samples were obtained for ZnTi $O_3$ at the sintering temperature range of 870~90$0^{\circ}C$ with B $i_2$ $O_3$ and $V_2$ $O_{5}$ additions of <1 wt.%, respectively. The microwave dielectric properties of ZnTi $O_3$ with 0.6 wt.% B $i_2$ $O_3$ and 0.5 wt.% $V_2$ $O_{5}$ were as follows: Qx $f_{o}$ = 48,400 GHz, $\varepsilon$$_{r}$= 22, and $\tau$$_{f}$ = -43 ppm/$^{\circ}C$. In order to improve temperature coefficient of resonant frequency, Ti $O_2$ was added to the abode system. The optimum amount of Ti $O_2$was 15 mol.% when sintered at 87$0^{\circ}C$, at which Ive could obtain following results: Qx $f_{O}$ = 44,700GHz, $\varepsilon$$_{r}$ = 26, and $\tau$$_{f}$ = 0 PPm/$^{\circ}C$.>.EX>.>.>.EX>.>.>.